RFR: 8316929: Shenandoah: Shenandoah degenerated GC and full GC need to cleanup old OopMapCache entries

[Zhengyu Gu]

During STW root scan, interpreted frame's oop map may be cached. But due to limited cache size (32 entries per instance class), entries may be evicted to old entries list due to collision, should be cleanup in VM_Operation's doit_epilogue(), or risk leaking memory.

Test:
  hotspot_gc_shenandoah (fastdebug and release on MacOSX)

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Commit messages:
 - 8316929: Shenandoah: Shenandoah degenerated GC and full GC need to cleanup old OopMapCache entries

Changes: https://git.openjdk.org/jdk/pull/15921/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=15921&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8316929
  Stats: 18 lines in 2 files changed: 13 ins; 0 del; 5 mod
  Patch: https://git.openjdk.org/jdk/pull/15921.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15921/head:pull/15921

PR: https://git.openjdk.org/jdk/pull/15921